There are increasing demands to develop a wideband phased array or electronically scanned array (ESA) that include a wide variety of configurations for various applications, such as satellite communications (SATCOM), radar, remote sensing, direction finding, and other systems. The goal is to provide more flexibility and functionality at reduced cost with consideration to limited space, weight, and power consumption (SWaP) on modern military and commercial platforms. This requires advances in ESA and manufacturing technologies.
A phased array antenna is an array of antenna elements in which the phases of respective signals feeding the antenna elements are set in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions, thus forming a beam. The relative amplitudes of constructive and destructive interference effects among the signals radiated by the individual elements determine the effective radiation pattern of the phased array. The number of antenna elements in a phased array antenna is often dependent on the required gain of a particular application and can range from dozens to tens of thousands or more.
Phased array antennas for ultra-wide bandwidth (more than one octave bandwidth) performance are often large, causing excessive size, weight, and cost for applications requiring many elements. The excessive size of an array may be required to accommodate “electrically large” radiating elements (several wavelengths in length), increasing the total depth of the array. Arrays may also be large due to the nesting of several multi-band elements to enable instantaneous ultra-wide bandwidth performance, which increases the total length and width of the array.
Phased arrays antennas have several primary performance characteristics in addition to the minimization of grating lobes, including bandwidth, scan volume, and polarization. Grating lobes are secondary areas of high transmission/reception sensitivity that appear along with the main beam of the phased array antenna. Grating lobes negatively impact a phased array antenna by dividing transmitted/received power into a main beam and false beams, creating ambiguous directional information relative to the main beam and generally limiting the beam steering performance of the antenna. Bandwidth is the frequency range over which an antenna provides useful match and gain. Scan volume refers to the range of angles, beginning at broadside (normal to the array plane) over which phasing of the relative element excitations can steer the beam without generating grating lobes. Polarization refers to the orientation or alignment of the electric field radiated by the array. Polarization may be linear (a fixed orientation), circular (a specific superposition of polarizations), and other states in between.
Phased array antenna design parameters such as antenna element size and spacing affect these performance characteristics, but the optimization of the parameters for the maximization of one characteristic may negatively impact another. For example, maximum scan volume (maximum set of grating lobe-free beam steering angles) may be set by the antenna element spacing relative to the wavelength at the high end of the frequency spectrum. Once cell spacing is determined, a desired minimum frequency can be achieved (maximizing bandwidth) by increasing the antenna element length to allow for impedance matching. However, increased element length may negatively influence polarization and scan volume. The scan volume can be increased through closer spacing of the antenna elements, but closer spacing can increase undesirable coupling between elements, thereby degrading performance. This undesirable coupling can change rapidly as the frequency varies, making it difficult to maintain a wide bandwidth.
Existing wide bandwidth phased array antenna elements are often large and require contiguous electrical and mechanical connections between adjacent elements (such as the traditional Vivaldi). In the last few years, there have been several new low-profile wideband phased array solutions, but many suffer from significant limitations. For example, planar interleaved spiral arrays are limited to circular polarization. Tightly coupled printed dipoles require superstrate materials to match the array at wide-scan angles, which adds height, weight, and cost. The Balanced Antipodal Vivaldi Antenna (BAVA) requires connectors to deliver the signal from the front-end electronics to the aperture.
Existing designs often have not been able to maximize phased array antenna performance characteristics such as bandwidth, scan volume, and polarization without sacrificing size, weight, cost, and/or manufacturability. Accordingly, there is a need for a phased array antenna with wide bandwidth, wide scan volume, and good polarization, in a low cost, lightweight, small footprint (small aperture) design that can be scaled for different applications.